The earliest relatives of "superbugs" — resistant to virtually all antibiotics — known as the enterococci, had evolved 450 million years ago, even before the dinosaurs, scientists say.
Currently, antibiotic resistance is a leading public health concern worldwide as it threatens nearly five per cent of patients with infections during their stay in hospitals, the researchers noted.
The findings showed evidence that enterococci were also in the intestines of land animals that are now extinct, including dinosaurs and the first millipede-like organisms to crawl onto land.
"By analysing the genomes and behaviours of today's enterococci, we were able to rewind the clock back to their earliest existence and piece together a picture of how these organisms were shaped into what they are today" said Ashlee M. Earl from the Broad Institute of the Massachusetts Institute of Technology (MIT) and Harvard.
In fact, the new species of enterococci appeared whenever new types of animals appeared.
This includes when new types of animals arose right after they first crawled onto land, and when new types of animals arose right after mass extinctions, especially the greatest mass extinction, the End Permian Extinction (251 million years ago), the researchers said, in the paper published in the journal Cell.
Further, all species of enterococci, including those that have never been found in hospitals, were found to be naturally resistant to dryness, starvation, disinfectants and many antibiotics.
"Understanding how the environment in which microbes live leads to new properties could help us to predict how microbes will adapt to the use of antibiotics, antimicrobial hand soaps, disinfectants and other products intended to control their spread," Earl added.